Bifocal lens



Patented May 23, I899.

J. L. BORSCH. BIFUCAL L ENS.

(Application mm Feb. 25, 1599.

(No Model.)

HQ 1. H6. Z- FIG. 51

UNITED STATES PATENT OFFICE.

JOHN L. BORSOH, OF PHILADELPHIA, PENNSYLVANIA.

BIFOCAL LENS.

SPECIFICATION forming part of Letters Patent No. 625,535, dated May 23,1899.

Application filed February 25, 1899. Serial No. 706.799. (No model.)

To all whom it may concern:

Be it known that 1, JOHN L. BORSOH, aciti zen of the United States,residing in the city and county of Philadelphia, in the State ofPennsylvania, have invented certain new and useful Improvements inBifocal Lenses, of which the following is a specification.

My invention relates to lenses, employed in spectacles and eye glasses,of the special character known as bifocal, that is to say, having twoindependent focal points located in the vicinity of each other, eachoccurring in one of the two regions into which the lens is divided,which respective regions are formed of such material and ground to suchconfiguration that their respective coefiicients of refraction are ofdissimilar power.

In practice bifocal lenses are employed by persons whose vision is ofsuch a character that a lens which enables them to see distant objectsdoes not enable them to see objects or print at close range, suchpersons being under the necessity either of employing two pairs ofglasses, one for distant and one for near vision, or of employing lensesof the character above set forth having distinct regions of dissimilarpowers of refraction.

Heretofore bifocal lenses have been frequently formed by matchinganduni-ting edge to edge two pieces of lens glass, each constituting butpart of a complete lens, and respectively suitably ground, the one fordistant and the other for near vision,and various forms have bydifferent constructors been given to the respective elements or sectionsof the lens, the only fixed requirement as to such-sections being thatthey should when united present as to their combined outer edges theusual oval outline of a lens.

In whatever forms the respective independent sections or elements of abifocal lens of the foregoing characterhave been made, however, theyhave been united by bringing the respective edges of said sections orelements into contact and cementing the abutting edges by any suitablebalsam or uniting medium, or maintaining them in their assembledposition by an inclosing lens frame.

This construction has been objectionable, however, by reason of the factthat however carefully the sections are assembled and cemented, a minutecement-filled space exists between the abuttingedges, and the. cementwhich is present of 'course on both surfaces of the lens, in timebecomes slightly worn away under the action of heat and the attrition towhich it is subjected in the cleaning of the lens, with the result thatthe permanence of the union between the elements or sections isimpaired; furthermore, the line of connection between the two sectionsof a bi focal lens as heretofore constructed as described is alwaysvisible, and not only detracts froin the appearance of the lens but isan annoyance to the wearer; furthermore, no matter how carefully thesections or elements are united it is practically impossible to preventone of the meeting edges of the sections from projecting slightly abovethe opposing edge of the other section, with the result that in thecleaning of the lens the projecting edge is very liable to be chipped.

WVhen, instead of uniting edge to edge two pieces of lens glass to forma bifocal lens, such lenses have been constructed by placing one pieceof lens glass upon the face of the other, the objections referred to arethe more pronounced.

Broadly stated, it is the object of my invention to produce a bifocallens of an attractive, efficient, and durable character, in which theobjections hereinbefore stated to the existing forms of such lensesshall be entirely obviated.

Generally expressed, my invention comprehends the provision of a lens ofusual outline, the body of which is composed of ordinary lens material,such as crown glass, and the faces of which are of any usual curvatureor form to produce any selected magnifying power or corrective effect tosuit the eyes of the wearer,-and herein termed the major lens,within asuitable recess in the interior of which lens is located a smaller lens,herein termed the minor lens,and whichis preferably formed of flintglass to constitute an element of index difierent from that of the majorlens, and the refractive power of which minor lens combined with therefractive power of that portion of the major lens In the usual form inwhich my lens will be constructed, as I contemplate, the major lens willbe a lens for distant vision and the minor lens will constitute acorrection of said lens (of an area equal to its own diameter) for nearvision.

The major and minor lenses may, of course, be of such form and relativeproportions as the constructor or user may prefer, and each may, asheretofore, be of any desired coefficient of refraction, theirrespective powers of refraction being entirely independent of each otherand capable of being made to conform to the requirements of any us ualform ula.

In following a prescribed formula to produce a given strength ofrefraction in the field of the minor lens, and which is composed as willbe understood, of said minor lens and the overlying portions of themajor lens bounded by the outline of said minor lens, a compoundcalculation, so to speak, will be required on the part of the lensgrinder, and it will be necessary for him to calculate the refractivepower to be possessed by that portion of the major-lens whichoverlies oris opposite to the minor lens, and to then conform or grind the insetminor lens to such shape that its refractive power plus the refractivepower of the ground glass in the overlying regions, will produce theaggregate refractive power prescribed.

The calculation referred to is one which any optician can readily makein accordance with known rules.

In the preferred construction of my improved bifocal lens I form themajor lens, whether it be the near lens or the distance lens, as twohalves, each preferably of approximately half the thickness of anordinary lens, and carefully grind or conform the opposing faces of therespective halves so that when brought into contact with each other theyshall accurately fit, and I also produce in one or both of said opposinginner faces,

according to the character of the lens employed, a recess of such formas to be adapted to receive the smaller or minor lens which is to beinclosed between the two halves of the major lens.

lVhen, then, the two halves of the major lens are, with the minor lenswithin the recess as stated, brought together and secured by balsam orotherwise, the result will be a compound lens of such conformation as topossess as to a selected portion of its area, a given coefficient ofrefraction, and the remaining portion of the area of which is, by thepresence in the interior of the structure of adistinct lenticular bodyof different index, of a distinct and different coefficient ofrefraction.

As will be understood, the respective halves of the lens may be of anypreferred shape as to their faces.

In the accompanying drawings,

Figure 1 is a vertical, transverse, sectional exhibit theirconstruction.

Figure 3 is a view similar to Figure 1, illustrating, however, a lensground to a different form.

Figure 4 is a view similar to Figure 3, the parts being slightlyseparated to more plainly exhibit their construction.

Figure 5 is a view in front elevation of a bifocal lens embodying myinvention.

Similar letters of reference indicate corresponding parts.

In the drawings,

A A indicate the respective halves or portions of the major lenses, andB the recess formed in the inner faces of the same, said recess is inFigures 1 and 2 shown as produced in the inner faces of both halves ofthe major lens, and in Figures 8 and 4 as produced altogether in one ofsaid halves. C is the minor lens.

As will be understood, a lens embodying my invention is uniform incurvature and in tegral in structure throughout all portions of eachface, so that not only is the presence of the inclosed minor lens notvisible except on very close inspection, but the presence of a joint orunion between the edges of the re spective elements on the surface ofthe lens is entirely avoided, with the result that the stateddisadvantages incident to the use of the well-known forms of bifocallenses are completely avoided.

I claim and desire to secure by Letters Patent 1. A bifocal lensconsisting of a major lens having faces which are each of selectedcurcontained within its interior, substantially as set forth.

2. A bifocal lens, consisting of amajorlens having faces which are eachof selected curvature and of eXteriorly uninterrupted struc* ture, and arelatively smaller minor lens contained within the interior of saidmajor lens, and the refractive power of which is combined with therefractive power of the overlying portions of the major lens to producein the region which it occupies a correction of the refractive power ofthe said majorlens, sub stantially as set forth.

3. A bifocal lens consisting of a major lens composed of two platesadapted to be placed face to face and secured together, each ground asto its outer face to any selected curvature, a recess between saidplates, and a minor lens disposed within said recess, substantially asset forth.

4. A bifocal lens consisting of a lens having faces which are each ofselected curvature or form and of exteriorly uninterrupted structure,and having within its interior a relatively smaller lens, the glass ofthe smaller lens being of index different from that of the larger,substantially as set forth.

5. Abifocal lens consisting of a major lens composed of two platesadapted to be placed face to face and secured together, each ground asto its outer face to any selected curvature, a recess between saidplates, and a minor lens disposed within said recess, said major lensand minor lens being formed of glass of dif- 1o ferent index,substantially as set forth.

In testimony that I claim the foregoing as my invention I have hereuntosigned my name this 21st day of February, A. D. 1899. r

JOHN L. BORSOH.

In presence of-- WM. M. CROWTHER', HAROLD G. KNIGHT.

